An absorbent article such as a pants-type disposable diaper and the like generally includes such members as waistline portions for the wearer's waistline (specifically, a front waistline portion and a back waistline portion), a crotch portion for the wearer's crotch, and an absorber which absorbs excretion discharged from the wearer. The pants-type diaper is provided with leg-surrounding portions where openings for inserting wearer's legs are formed. Each of the leg-surrounding portions is provided with a leg gather formed with a string-like rubber to fit the leg-surrounding portion to the wearer.
In a manufacturing process of such a pants-type diaper, a web including a continuum of the members described above is conveyed using conveyor belts and the like. In a web folding step, a web is folded into two in the cross direction CD orthogonal to the machine direction MD so that a continuum of front waistline portions and a continuum of back waistline portions can be overlaid one another, while the web provided with leg-surrounding portions is being conveyed in the machine direction MD, that is, in a flow direction of the manufacturing process (Patent Document 1, for example).
Next, in a web joining step, the front waistline portions are joined to the back waistline portions at a predetermined intervals by using a joint apparatus provided with a ultrasonic horn and an anvil roll while the web folded in two are continuously being conveyed in the machine direction (Patent Document 2, for example). Then, in a cutting step, the web is cut into individual pants-type diapers by using a cutting apparatus provided with a cutting blade.
Since leg gathers are provided at the leg-surrounding portions of the web folded into two, the vicinity of the leg-surrounding portions of the web is likely to contract in the cross direction. For this reason, when the doubled web is joined in the joining step with the vicinity of the leg-surrounding portion contracted in the cross section, a crease is likely to occur at a joint portion of the front waistline portion and the back waistline portion, thereby causing a problem of manufacture defects of the absorbent article.
In the joining step, the web is conveyed along outer peripheral surface of the anvil rolls. Also, since an absorber is provided to the crotch portion of the web, the crotch portion is heavier in weight than the waistline portions. Therefore, the crotch portion of the web is likely to float off from the anvil rolls when the crotch portion contracts toward the waistline portions due to contraction of the leg gathers.
As a result, when the web is conveyed along the outer peripheral of the anvil roll, the crotch portion may curl up due to a centrifugal force in a direction in which the crotch portion gets away from the anvil roll, that is, in the normal direction of the anvil roll. At this time, the curled crotch portion may touch the ultrasonic horn or may be clogged in a gap between the ultrasonic horn and the anvil roll, whereby causing manufacture defect of the absorbent article.